Electrochromic Metallo-Organic Nanoscale Films: Fabrication, Color Range, and Devices

In this study, we demonstrate a versatile
approach for the formation
of electrochromic nanoscale assemblies on transparent conductive oxides
on both rigid and flexible substrates. Our method is based on the
application of alternating spin-coated layers of well-defined metal
polypyridyl complexes and a palladium­(II) salt to form electrochemically
addressable films with a high chromophore density. By varying the
central metal ion of the polypyridyl complexes (Os, Ru, and Fe) and
their ligands and by mixing these complexes, coatings with a wide
range of colors can be achieved. These coatings cover a large area
of RGB color space. The coloration intensities of these nanoscale
films can be tuned by the number of deposition steps. The materials
have very attractive ON/OFF ratios, electrochemical stabilities, and
coloration efficiencies. Reversible color-to-colorless and color-to-color
transitions were demonstrated, and the films were further integrated
into sandwich cells.